Jump to content

Necessary with engine breather valve on GT6?


Recommended Posts

Hi all!

My newly purchased 1971 GT6 Mk3 don't have the engine breather valve installed. Instead, the breather hose is connected to a simple oil separator which in turn is connected to the inlet manifold. This puts the entire engine under the same vacuum as the inlet manifold.

As a temporary solution, I have blinded the hose to the inlet manifold and vented the oil separator to athmosphere.

Any toughts on the one solution or the other or should I install a breather valve ASAP?

Link to comment
Share on other sites

A pressurised engine will naturally leak some more oil but how do excess vacuum affect the engine? Since all engines I know either have a breather valve or vent to air filter, I guess the breather valve is the way to go, I certainly don't want oil fumes fed into my Strombergs...

Link to comment
Share on other sites

The GT6 Mk3's didn't have breather valves like the earlier GT6's that had the breather hose routed from the valve cover to a connector in the center of the intake manifold.  The Mk3 breather hose ran from the valve cover to Y to connect to large vacuum intakes on the carbs, and then somewhere also Y'd off to connect to a charcoal canister.

It actually works well.  I have never thought to investigate where the breather connections on the Strombergs are located in the general scheme of the carb design, but it doesn't put oil in sensitive places like the needle/jet interface or the dashpot area.

Link to comment
Share on other sites

Ok, thanks.

It seems that the engine is supposed to be under full vacuum then.

As long as the breather hose is connected to the intake manifold, the carbs is not contaminated. Many other (older) cars have the breather hose connected between the air filter and carb, don't think the Strombergs would like that...

Link to comment
Share on other sites

You can sort of mix engines from different years, but the important points for connection are:
1) is there a breather connection located on top of the intake manifold or not
2) Do the carbs each have the large breather connections at the back of each one

Here is an engine with the breather connection on top of the intake manifold; the carbs do not have built into them connections for the fat breather hose.  It uses a valve.  The valve is the big round thing in the hose near the intake manifold, it has SMITHS marked on the top:

Here is a later engine without the breather connection on top of the intake manifold, the carbs are the type that have built into them connections for the fat breather hose on the back.  It does not use a valve:

The carbs with the breather hose in the back do not get a mess inside them from the breather connection.

That is the basic setup, although things may be arranged differently.
If the car had the optional a brake vacuum booster, there is another Y in the fat hoses to send a fat hose to the brake vacuum booster.

My car did not have a brake vacuum booster, but the charcoal canister/oil separator was not located in the place shown, but was located on the firewall where the brake booster would have gone, not in front of the front carb as seen in the picture.

See if there is a small, pencil-size line going back to the fuel tank area that is not the fuel line.  If it is present, it connects to a separate port on the canister/oil separator.

Link to comment
Share on other sites

Your GT6 is very interesting!

It looks like the breathing components & setup have been changed from the original setup, so you might get better advice from some of the others here who do the same.  It looks like you have an oil "catch can" as some others do, & not the original charcoal canister arrangement.

Your videos will sound much better when all 6 cylinders wake up:

Link to comment
Share on other sites

My car don't have the original engine, it broke down and were swapped with a rebuilt one. Don't know the story about this one other than that it were sold to previous owner by a swede.

My vent hoses look like this:

Note the one hose I disconnected and blinded. The shiny canister is a kind of oil separator filled with wire mesh.

@rotoflex: The bonnet is made of fibreglass and the air intakes is homemade by previous owner. They are very nice craftmanship but I would prefer not to have those two triangular ones in the front... And it runs nice on all 6 now, as also described in the video text. One dirty sparkplug let cyl #2 down...

Link to comment
Share on other sites

Also examine the carbs to see if they are the type that had connections for the breather hose.
If those connections are present, they will need to be blocked off in your current setup.

Here are a couple of pictures of GT6Craig's carbs so you can see where to look for the connections:

Did the new engine come with its own carbs, or do you still have the carbs that came with the car?
The car originally came with the carbs that had connections for the breather hose, but they may have been changed in the past.
In fact, your carbs do look like the earlier carbs that had moveable jets for chokes, & no connections for the breather hose.

Link to comment
Share on other sites

I have one spare set of inlet manifold with two carbs but I think all the carbs are equal. They all have a small choke damper that lifts the piston/needle a bit to enrichen the mixture. Nozzle adjustment is below the carb thru the float chamber. I haven't noted the vent connections on either of these...

Link to comment
Share on other sites

I believe you may find the choke functions on those by moving the jet that the needle fits into at the bottom.
Breather connections should not be present on the carb type that chokes as you describe.

Those carbs are a little easier to tune than the later ones, & you are likely to be more pleased with them.
I think the only dissatisfaction sometimes comes from the plastic breaking on the connecting shafts between the carbs.
You may expect if you are reading a workshop manual that, for you, the carb procedures are more likely to be for GT6 Mk2 rather than GT6 Mk3.

i hear your electric fuel pump, but you must be polite & also show us a picture of the side with the distributor.
If you are interested:  since you are not using the mechanical fuel pump, some have put a breather over the location of the mechanical fuel pump.  Some have not.  I believe Kas Kastner did sometimes.

Link to comment
Share on other sites

The mechanical fuel pump is still installed but not in use as it gave far too high pressure so the carbs overflowed. I intend to remove it and blind that hole. I now have an electrical pump that is speced to 0.1 bar/1.45 PSI but in real life it is more like 0.15 bar/2.17 PSI but that is ok. I'll have a couple of pictures for you tonight :-)

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...